1. The problem statement, all variables and given/known data In one type of mass spectrometer the ions are passed through a velocity selector. This is a pair of parallel plates 2.5 cm apart. A pd of 140 V is applied to create an electric field. A magnetic field is also applied so as to give a force in the direction opposite to the field. Calculate the magnetic field strenght needed to allow uni-positive (loss of 1 electron) neon-20 ions (mass = 3.32 * 10-26) to pass un-deflected through a velcoity selector The neon-20 ions are moving at 3 * 105 ms-1 2. Relevant equations 3. The attempt at a solution So I think the way to do this is to equate BqV = mv2/r so B = mv2/rqV B = 10671.428... T (using a radius of 2.5/200) The answer given is 1.8 * 10-2 T How??